Optical sensor using collimator

ABSTRACT

Systems and methods for optical imaging are disclosed. The optical fingerprint sensor includes an image sensor array; a collimator filter layer disposed above the image sensor array, the collimator filter layer having an array of apertures; and an illumination layer disposed above the collimator filter layer. The collimator filter layer filters reflected light such that only certain of the reflected light beams reach optical sensing elements in the image sensor array. Employing the collimator filter layer prevents blurring while allowing for a lower-profile image sensor

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/111,012, filed on Feb. 2, 2015, the entirecontents of which are expressly incorporated by reference.

FIELD

This disclosure generally relates to optical sensors, and moreparticularly to an optical sensor using a collimator.

BACKGROUND

Object imaging is useful in a variety of applications. By way ofexample, biometric recognition systems image biometric objects forauthenticating and/or verifying users of devices incorporating therecognition systems. Biometric imaging provides a reliable,non-intrusive way to verify individual identity for recognitionpurposes. Various types of sensors may be used for biometric imaging.

Fingerprints, like various other biometric characteristics, are based ondistinctive personal characteristics and thus provide a reliablemechanism to recognize an individual. Thus, fingerprint sensors havemany potential applications. For example, fingerprint sensors may beused to provide access control in stationary applications, such assecurity checkpoints. Fingerprint sensors may also be used to provideaccess control in mobile devices, such as cell phones, wearable smartdevices (e.g., smart watches and activity trackers), tablet computers,personal data assistants (PDAs), navigation devices, and portable gamingdevices. Accordingly, some applications, in particular applicationsrelated to mobile devices, may require recognition systems that are bothsmall in size and highly reliable.

Most commercially available fingerprint sensors are based on optical orcapacitive sensing technologies. Unfortunately, conventional opticalfingerprint sensors are too bulky to be packaged in mobile devices andother common consumer electronic devices, confining their use to dooraccess control terminals and similar applications where sensor size isnot a restriction.

As a result, fingerprint sensors in most mobile devices are capacitivesensors having a sensing array configured to sense ridge and valleyfeatures of a fingerprint. Typically, these fingerprint sensors eitherdetect absolute capacitance (sometimes known as “self-capacitance”) ortrans-capacitance (sometimes known as “mutual capacitance”). In eithercase, capacitance at each sensing element in the array varies dependingon whether a ridge or valley is present, and these variations areelectrically detected to form an image of the fingerprint.

While capacitive fingerprint sensors provide certain advantages, mostcommercially available capacitive fingerprint sensors have difficultysensing fine ridge and valley features through large distances,requiring the fingerprint to contact a sensing surface that is close tothe sensing array. It remains a significant challenge for a capacitivesensor to detect fingerprints through thick layers, such as the thickcover glass (sometimes referred to herein as a “cover lens”) thatprotects the display of many smart phones and other mobile devices. Toaddress this issue, a cutout is often formed in the cover glass in anarea beside the display, and a discrete capacitive fingerprint sensor(often integrated with a mechanical button) is placed in the cutout areaso that it can detect fingerprints without having to sense through thecover glass. The need for a cutout makes it difficult to form a flushsurface on the face of device, detracting from the user experience, andcomplicating the manufacture. The existence of mechanical buttons alsotakes up valuable device real estate.

One possible solution for an optical based sensor is to use a pinholetype camera. A pinhole camera includes a thin light blocking layer witha small aperture. Light from an object on one side of the blocking layerpasses through the aperture and is projected in an inverted fashion ontoa detection surface disposed on the opposite side of the blocking layer.However, pinhole cameras suffer from certain disadvantages. For example,images collected from a pinhole camera arrangement are inverted and thusmay require additional processing to be useful. Moreover, the vastamount of light from the object is blocked by the blocking layer andonly a small amount of light is transmitted through the aperture. Thus,image quality may be an issue. Moreover, the area of the object imagedvaries significantly as the distance between the blocking layer and theobject to be imaged varies.

SUMMARY

One embodiment of the disclosure provides an optical fingerprint sensor.The optical fingerprint sensor includes an image sensor array; acollimator filter layer disposed above the image sensor array, thecollimator filter layer having an array of apertures; and anillumination layer disposed above the collimator layer.

Another embodiment of the disclosure provides an optical fingerprintsensor. The optical fingerprint sensor includes an illumination layerconfigured to direct light to a sensing region; a collimating layer,disposed below the illumination layer, and including a plurality ofapertures, wherein the apertures are configured to block a portion oflight from the illumination layer; and an image sensor layer, disposedbelow the collimating layer, and including an array of optical sensorelements arranged so that a plurality of the sensor elements receivelight transmitted through one of the plurality of apertures.

Yet another embodiment of the disclosure provides a method of imaging afingerprint using a device. The method includes transmitting light in anillumination region such that at least a portion of light reflects froma sensing region; blocking at least a first portion of the lightreflected from the sensing region at a surface of a collimating layer;blocking at least a second portion of the light reflected from thesensing region within a plurality of apertures of the collimating layer;and sensing, at a plurality of optical sensor elements in a sensorarray, a third portion of light reflected from the sensing region, thethird portion of light being passed through at least one of theplurality of apertures in the collimating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a system that includes anoptical sensor and a processing system, according to an embodiment ofthe disclosure.

FIG. 2 illustrates an example of a mobile device that includes anoptical sensor according to an embodiment of the disclosure.

FIG. 3 illustrates an example of an optical sensor with a collimatorfilter layer according to an embodiment of the disclosure.

FIG. 4 illustrates an example of light interacting with an opticalsensor having a collimator filter layer according to an embodiment ofthe disclosure.

FIG. 5 illustrates an alternative embodiment of a collimator filterlayer according to an embodiment of the disclosure

FIG. 6 illustrates a method of imaging an input object according to anembodiment of the disclosure.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, summary, brief description of the drawings, or the followingdetailed description.

Turning to the drawings, and as described in greater detail herein,embodiments of the disclosure provide methods and systems to opticallyimage an input object such as a fingerprint. In particular, a method andsystem is described wherein an optical sensor includes a collimatorfilter layer which operates as a light conditioning layer, interposedbetween a light illumination layer and an image sensor array.Transmitted light from the illumination layer reflects from an inputobject in a sensing region above a cover layer. The reflected light isfiltered by the collimator filter layer such that only certain of thereflected light beams reach optical sensing elements in the image sensorarray.

Employing the collimator filter layer of the present disclosure preventsblurring while allowing for a lower-profile image sensor, such as afingerprint sensor, than is possible with purely lens-based or pinholecamera based imaging sensors. Thus, the image sensor can be made thinfor use in mobile devices such as cell phones. Placing individualcollimator apertures over each optical sensing element, or group ofelements, provides better sensitivity than purely pinhole based imagersby transmitting more light to the optical sensing elements. The presentdisclosure describes the use of the collimator filter layer to enableoptical sensing through a large range of thicknesses of cover layers.

FIG. 1 is a block diagram of an example of an electronic system 100 thatincludes an optical sensor device 102 and a processing system 104,according to an embodiment of the disclosure. By way of example, basicfunctional components of the electronic device 100 utilized duringcapturing, storing, and validating a biometric match attempt areillustrated. The processing system 104 includes a processor(s) 106, amemory 108, a template storage 110, an operating system (OS) 112, and apower source(s) 114. Each of the processor(s) 106, the memory 108, thetemplate storage 110, and the operating system 112 are interconnectedphysically, communicatively, and/or operatively for inter-componentcommunications. The power source 114 is interconnected to the varioussystem components to provide electrical power as necessary.

As illustrated, processor(s) 106 are configured to implementfunctionality and/or process instructions for execution withinelectronic device 100 and the processing system 104. For example,processor 106 executes instructions stored in memory 108 or instructionsstored on template storage 110 to identify a biometric object ordetermine whether a biometric authentication attempt is successful orunsuccessful. Memory 108, which may be a non-transitory,computer-readable storage medium, is configured to store informationwithin electronic device 100 during operation. In some embodiments,memory 108 includes a temporary memory, an area for information not tobe maintained when the electronic device 100 is turned off. Examples ofsuch temporary memory include volatile memories such as random accessmemories (RAM), dynamic random access memories (DRAM), and static randomaccess memories (SRAM). Memory 108 also maintains program instructionsfor execution by the processor 106.

Template storage 110 comprises one or more non-transitorycomputer-readable storage media. In the context of a fingerprint sensor,the template storage 110 is generally configured to store enrollmentviews for fingerprint images for a user's fingerprint or otherenrollment information. More generally, the template storage 110 may beused to store information about an object. The template storage 110 mayfurther be configured for long-term storage of information. In someexamples, the template storage 110 includes non-volatile storageelements. Non-limiting examples of non-volatile storage elements includemagnetic hard discs, solid-state drives (SSD), optical discs, floppydiscs, flash memories, or forms of electrically programmable memories(EPROM) or electrically erasable and programmable (EEPROM) memories,among others.

The processing system 104 also hosts an operating system (OS) 112. Theoperating system 112 controls operations of the components of theprocessing system 104. For example, the operating system 112 facilitatesthe interaction of the processor(s) 106, memory 108 and template storage110.

According to various embodiments, the processor(s) 106 implementhardware and/or software to obtain data describing an image of an inputobject. The processor(s) 106 may also align two images and compare thealigned images to one another to determine whether there is a match. Theprocessor(s) 106 may also operate to reconstruct a larger image from aseries of smaller partial images or sub-images, such as fingerprintimages when multiple partial fingerprint images are collected during abiometric process, such as an enrollment or matching process forverification or identification.

The processing system 104 includes one or more power sources 114 toprovide power to the electronic device 100. Non-limiting examples ofpower source 114 include single-use power sources, rechargeable powersources, and/or power sources developed from nickel-cadmium,lithium-ion, or other suitable material as well power cords and/oradapters which are in turn connected to electrical power.

Optical sensor 102 can be implemented as a physical part of theelectronic system 100, or can be physically separate from the electronicsystem 100. As appropriate, the optical sensor 102 may communicate withparts of the electronic system 100 using any one or more of thefollowing: buses, networks, and other wired or wirelessinterconnections. In some embodiments, optical sensor 102 is implementedas a fingerprint sensor to capture a fingerprint image of a user. Inaccordance with the disclosure, the optical sensor 102 uses opticalsensing for the purpose of object imaging including imaging biometricssuch as fingerprints. The optical sensor 102 can be incorporated as partof a display, for example, or may be a discrete sensor.

Some non-limiting examples of electronic systems 100 include personalcomputers of all sizes and shapes, such as desktop computers, laptopcomputers, netbook computers, tablets, web browsers, e-book readers, andpersonal digital assistants (PDAs). Additional example electronicsystems 100 include composite input devices, such as physical keyboardsand separate joysticks or key switches. Further example electronicsystems 100 include peripherals such as data input devices (includingremote controls and mice) and data output devices (including displayscreens and printers). Other examples include remote terminals, kiosks,video game machines (e.g., video game consoles, portable gaming devices,and the like), communication devices (including cellular phones, such assmart phones), and media devices (including recorders, editors, andplayers such as televisions, set-top boxes, music players, digital photoframes, and digital cameras).

The optical sensor 102 may provide illumination to the sensing region.Reflections from the sensing region in the illumination wavelength(s)are detected to determine input information corresponding to the inputobject.

The optical sensor 102 may utilize principles of direct illumination ofthe input object, which may or may not be in contact with a sensingsurface of the sensing region depending on the configuration. One ormore light sources and/or light guiding structures may be used to directlight to the sensing region. When an input object is present, this lightis reflected from surfaces of the input object, which reflections can bedetected by the optical sensing elements and used to determineinformation about the input object.

The optical sensor 102 may also utilize principles of internalreflection to detect input objects in contact with a sensing surface.One or more light sources may be used to direct light in a light guidingelement at an angle at which it is internally reflected at the sensingsurface of the sensing region, due to different refractive indices atopposing sides of the boundary defined by the sensing surface. Contactof the sensing surface by the input object causes the refractive indexto change across this boundary, which alters the internal reflectioncharacteristics at the sensing surface, causing light reflected from theinput object to be weaker at portions where it is in contact with thesensing surface. Higher contrast signals can often be achieved ifprinciples of frustrated total internal reflection (FTIR) are used todetect the input object. In such embodiments, the light may be directedto the sensing surface at an angle of incidence at which it is totallyinternally reflected, except where the input object is in contact withthe sensing surface and causes the light to partially transmit acrossthis interface. An example of this is presence of a finger introduced toan input surface defined by a glass to air interface. The higherrefractive index of human skin compared to air causes light incident atthe sensing surface at the critical angle of the interface to air to bepartially transmitted through the finger, where it would otherwise betotally internally reflected at the glass to air interface. This opticalresponse can be detected by the system and used to determine spatialinformation. In some embodiments, this can be used to image small scalefingerprint features, where the internal reflectivity of the incidentlight differs depending on whether a ridge or valley is in contact withthat portion of the sensing surface.

FIG. 2 illustrates an example of a electronic device 116, such as amobile phone, which includes cover glass 118 over a display 120. Thedisclosed method and system may be implemented by using the display 120as the optical sensor to image an input object. Alternatively, aseparate discrete component 122 provides the optical sensingcapabilities. A discrete sensor may provide more flexibility indesigning the optical components of the sensor for optimum illuminationand/or signal conditioning than when attempting to integrate the opticalsensor components on a display substrate, such as a TFT backplane.

FIG. 3 illustrates an example of a stack-up for an optical image sensordevice 200 used to image an object 216, such as a fingerprint. Thesensor 200 includes an image sensor array 202, a collimator filter layeror light conditioning layer 204 disposed above the image sensor array202, an illumination layer 207 disposed above the collimator filterlayer 204, a light source 208, and a cover layer 210. In certainembodiments, a blocking layer 214 may also be provided.

The cover layer 210 protects the inner components of the sensor 200 suchas the image sensor array 202. The cover layer 210 may include a coverglass or cover lens that protects inner components of a display inaddition to the sensor 200. A sensing region for the input object isdefined above the cover layer 210. A top surface 218 of the cover layer210 may form a sensing surface, which provides a contact area for theinput object 216 (e.g., fingerprint). The cover layer 210 is made of anymaterial such as glass, transparent polymeric materials and the like.

Although generally described in the context of fingerprint forillustrative purposes, the input object 216 is any object to be imaged.Generally, the object 216 will have various features. By way of example,the object 216 has ridges and valleys. Due to their protruding nature,the ridges contact the sensing surface 218 of the cover 210 layer. Incontrast, the valleys do not contact the sensing surface 218 and insteadform an air gap between the input object 216 and the sensing surface218. The object 216 may have other features such as stain, ink and thelike that do not create significant structural differences in portionsof the input object 216, but which affect its optical properties. Themethods and systems disclosed herein are suitable for imaging suchstructural and non-structural features of the input object 216.

The illumination layer 207 includes a light source 208 and/or a lightguiding element 206 that directs illumination to the sensing region inorder to image the input object. As shown in FIG. 3, the light source208 transmits beams or rays of light 212 into the light guiding element206 and the transmitted light propagates through the light guidingelement 206. The light guiding element may utilize total internalreflection, or may include reflecting surfaces that extract light uptowards the sensing region. Some of the light in the illumination layermay become incident at the sensing surface 218 in an area that iscontact with the input object 216. The incident light is in turnreflected back towards the collimator filter layer 204. In the exampleshown, the light source 208 is disposed adjacent to the light guidingelement 206. However, it will be understood that the light source 208may be positioned anywhere within the sensor 200 provided that emittedlight reaches the light guiding element 206. For example, the lightsource 208 may be disposed below the image sensor array 202. Moreover,it will be understood that a separate light guiding element 206 is notrequired. For example, the light transmitted from the light source 208can be transmitted directly into the cover layer 210 in which case thecover layer 210 also serves as the light guiding element. As anotherexample, the light transmitted from the light source 208 can betransmitted directly to the sensing region, in which case the lightsource 208 itself serves as the illumination layer.

A discrete light source is also not required. For example, the methodand system contemplate using the light provided by a display or thebacklighting from an LCD as suitable light sources. The light providedby the illumination layer 207 to image the object 216 may be in nearinfrared (NIR) or visible. The light can have a narrow band ofwavelengths, a broad band of wavelengths, or operate in several bands.

The image sensor array 202 detects light passing through the collimatorfilter layer 204. Examples of suitable sensor arrays are complimentarymetal oxide semiconductor (CMOS) and charge coupled device (CCD) sensorarrays. The sensor array 202 includes a plurality of individual opticalsensing elements capable of detecting the intensity of incident light.

To achieve optical sensing of fingerprints and fingerprint-sizedfeatures through thicker cover layers 210, light reflected from thefingerprint is conditioned by the light collimator filter layer 204 sothat the light reaching a sensing element in the image sensor array 202comes only from a small spot on the input object 216 directly above thesensor element. In the absence of such conditioning, any light arrivingat a sensing element from a region on the object far away from theoptical sensing elements contributes to image blurring.

To condition the light in accordance with the disclosure, the collimatorfilter layer 204 is provided with an array of apertures, or collimatorholes, 220 with each aperture being directly above one or more opticalsensing elements on the image sensor array 202. The apertures 220 areformed using any suitable technique, such as laser drilling, etching andthe like.

The collimator filter layer 204 only allows light rays reflected fromthe input object 216 (e.g., finger) at normal or near normal incidenceto the collimator filter layer 204 to pass and reach the optical sensingelements of the image sensor array 204. In one embodiment, thecollimator filter layer 204 is an opaque layer with array of holes 220.The collimator filter layer 204 is laminated, stacked, or built directlyabove the image sensor array 202. By way of example, the collimatorfilter layer 204 may be made of plastics such as polycarbonate, PET,polyimide, carbon black, inorganic insulating or metallic materials,silicon, or SU-8. In certain embodiments, the collimator filter layer204 is monolithic.

Also shown in FIG. 3 is blocking layer 214, which is optionally providedas part of optical sensor 200. The blocking layer 214 is asemitransparent or opaque layer that may be disposed above thecollimator filter layer 204. By way of example, the blocking layer maybe disposed between the cover layer 210 and the illumination layer 207,as shown in FIG. 3. Alternatively, the blocking layer 214 may bedisposed between the illumination layer 207 and the collimator filterlayer 204. In either case, the blocking layer 214 obscures components ofthe sensor 200, such as the apertures in the collimator filter layer,from ambient light illumination, while still allowing the sensor 200 tooperate. The blocking layer 214 may include of a number of differentmaterials or sub-layers. For example, a thin metal or electronconducting layer may be used where the layer thickness is less than theskin depth of light penetration in the visible spectrum. Alternately,the blocking layer 214 may include a dye and/or pigment or several dyesand/or pigments that absorb light, for example, in the visible spectrum.As yet another alternative, the blocking layer 214 may include severalsub-layers or nano-sized features designed to cause interference withcertain wavelengths, such as visible light for example, so as toselectively absorb or reflect different wavelengths of light. The lightabsorption profile of the blocking layer 214 may be formulated to give aparticular appearance of color, texture, or reflective quality therebyallowing for particular aesthetic matching or contrasting with thedevice into which the optical sensor 200 is integrated. If visibleillumination wavelengths are used, a semitransparent layer may be usedto allow sufficient light to pass through the blocking layer to thesensing region, while still sufficiently obscuring components below.

FIG. 4 illustrates a closer view of the collimator filter layer 204disposed between the illumination layer 207 and the image sensor array202 and interaction of light within the sensor 200. Portions 226 of thecover layer 210 are in contact with ridges of the input object 216 andportion 228 of the cover layer 210 is in contact with air due to thepresence of a valley of object 216. Image sensor array 202 includesoptical sensing elements 230, 232, 234 and 236 disposed below aperturesor holes 220 of the collimator filter layer 204.

Illustratively shown are a series of light rays reflected at the coverlayer 210. For example, light rays 238 reflect from the cover layer 210at portions occupied by ridges or valleys of the object 216. Because thelight rays 238 are above collimator apertures 220 and are relativelynear normal, the light rays 238 pass through the apertures 220 in thecollimator filter layer 204 and become incident on optical sensingelements 232 and 236, for example. The optical sensing elements can thenbe used to measure the intensity of light and convert the measuredintensity into image data of the input object 216. On the other hand,light beams 240 and 242, which have a larger angle from normal, strikethe collimator filter layer 204, either on its top surface or at surfacewithin the aperture (e.g., aperture sidewall) and are blocked andprevented from reaching optical sensing elements in the image sensorarray 202.

A metric of the collimator filter layer 204 is an aspect ratio of theapertures or holes 220. The aspect ratio is the height of the holes (h)244 in the collimator filter layer 204 divided by hole diameter (d) 246.The aspect ratio should be sufficiently large to prevent “stray” lightfrom reaching the optical sensing elements directly under eachcollimator hole. An example of stray light is light ray 242 reflectedfrom portion 228 of the cover layer 210 (e.g., a valley), which wouldreach sensing elements underneath a ridge in the absence of thecollimator filter layer. Larger aspect ratios restrict the lightacceptance cone to smaller angles, improving the optical resolution ofthe system. The minimum aspect ratio can be estimated using a ratio ofthe distance from the collimator filter layer 204 to the object beingimaged (e.g., finger) divided by the desired optical resolution of thefinger. In some embodiments, the collimator apertures 220 arecylindrical or conical in shape. The sidewalls of the collimatorapertures 220 may include grooves or other structures to prevent straylight from reflecting off the walls and reaching the optical sensingelements. The effective aspect ratio is determined by the average holediameter along height of the collimator holes. Examples of suitableaspect ratios are ratios in the range of about 3:1 to 100:1 and moretypically in the range of about 5:1 to 20:1.

It is generally desirable to make the height 244 of the collimatorapertures 220 as thin as possible to provide the most flexibility forfabricating the collimator filter layer 204 and integrating it with theunderlying image sensor array 202, such as a CMOS or CCD image sensor. Asmall aperture diameter 246 may be used to maintain the desiredcollimator aspect ratio. However, if the aperture is made too small(less than a few times the wavelength of light being used), diffractioneffects can contribute to additional blurring as the light rays exitingthe collimator apertures 220 diverge. Such diffraction effects can bemitigated by placing the collimator filter layer 204 as close to theimage sensor array 202 as possible, ideally much closer than theFraunhofer far field distance (r̂2/lambda, where r is the aperture radiusand lambda is the light wavelength).

It is also generally desirable to minimize the distance between thecollimator filter layer 204 and the image sensor array 202 to allow thelight reaching the optical sensing elements of the image sensor array202 to be as concentrated as possible. In addition, if this sensor array202 to collimator filter layer 204 distance is too large, stray lightfrom adjacent holes may reach a particular optical sensing element,contributing to image blurring.

If the image sensor array 202 is a CCD or CMOS image sensor, where theoptical sensing element pitch (distance between elements) may be smallerthan the collimator hole pitch (distance between holes), the lightpassing through a single collimator aperture 220 may illuminate morethan one optical sensing element. Such an arrangement is shown byoptical sensing elements 234 and 236 in FIG. 4. In such cases, theprocessing system (FIG. 1) may combine the light intensity recorded byall the optical sensing elements corresponding to a given collimatoraperture. The resulting fingerprint image after processing raw data fromthe image sensor array 202 may have a resolution corresponding to thearray of collimator apertures. It will be noted that the arrangement ofapertures 220 in the collimator filter layer 204 may result in someoptical sensing elements in the sensor array 202 going unused. Examplesof an unused optical sensing elements are sensing elements 240. Becauseoptical sensing elements 240 are not underneath a collimator hole,reflected rays will be blocked before reaching them. Image processingmay remove the unused sensor elements and scale the image appropriatelybefore the data is used in image reconstruction or image matching, forexample.

The imaging resolution (in dpi) of the optical sensor 200 is defined bythe resolution of the apertures 220 in the collimation filter layer 204whereas the pitch is the distance between each aperture. In the opticalsensor 200, each aperture 220 in the collimator filter layer 204corresponds to a sample of a feature of the object 216 being imaged,such as a sample from a ridge or valley within a fingerprint. Tomaximize resolution, the sampling density (which is equal to theaperture density) should be large enough such that multiple samples aretaken of each feature of interest. Thus, for example, to image ridges ina fingerprint, the pitch may be on the order of 50 to 100 microns sincethe pitch of the ridges themselves is on the order of 150 to 250microns. If it desired to capture more granular features, such as poresin a fingerprint, a smaller pitch such as 25 microns would beappropriate. Conversely, a larger pitch can be used to capture largerfeatures of the input object.

The optical sensor 200 performs similarly over a wide range of distancesbetween the collimator filter layer 204 and the sensing surface 220because the filtering of reflected light is generally thicknessindependent, as long as the aspect ratio of the holes in the collimatorfilter layer 204 is chosen to support the desired optical resolution.

FIG. 5 shows an alternative embodiment of the collimator filter layer204. As described above, the collimator filter layer 204 is made oflight-absorbing materials and includes an array of apertures 220. In thealternative embodiment shown, the top surface of the collimator filterlayer 204 further includes a reflecting layer 250. The reflecting layer250 allows light beams which would normally be absorbed by thecollimator filter layer 204 to be reflected back upwards towards thesensing region. Redirecting the light back to the sensing region allowsthe reflected light to be recycled so that some of the recycled lightcan be reflected off the input object to be imaged and transmittedthrough the collimator filter layer apertures.

Inclusion of the reflecting layer 250 minimizes light loss by reflectingthe stray light back to the input object 216 without requiring a highlevel of illumination in the overall sensor package. The top of thelight-absorbing collimator filter layer body may be roughened up usingvarious texturizing techniques, including but not limited to,sandblasting, coating with fillers, UV embossing or dry etching. Thisroughened-up top may then covered with a thin layer of metal, whichcreates a surface that is multifaceted in a randomized fashion. Thereflecting layer 250 may be made of any suitable material that willreflect light such as aluminum, chromium, and silver to name a fewexamples.

The method and system disclosed contemplate various ways to include thecollimator filter layer 204 into the overall structure of the opticalsensor 200. For example, the collimator filter layer 204 may be apre-patterned structure that is laminated or stacked onto the imagesensor array 202, as generally depicted in FIGS. 3-4. Alternativeembodiments are contemplated by present disclosure. For example, onealternative embodiment is to pattern or create the collimator filterlayer 204 directly onto a CMOS image sensor die or wafer, as generallydepicted in FIG. 5. For example, a wafer-level collimator layer may beformed by micro-fabrication. Instead of placing a separate collimatorfilter layer 204 on top of the image sensor array 202, back-endprocesses are added to CMOS image sensor array fabrication. With thistechnique, no separate manufacturing of the collimator filter layer isrequired. On top of the CMOS image sensor array, liquid-type polymerresin with light-absorbing dyes such as carbon black may be coated firstthen cured to form the collimator filter layer body. After the polymerresin is cured, metal may be optionally sputtered onto the cured resintop to act as a reflective layer. The aperture pattern may be madethrough photolithography and etching of the metal and the polymer layerunderneath subsequently to create the apertures. As a final step, themetal layer can be roughened up to create a reflecting/diffusing layer.

In yet another embodiment, the collimator filter layer 204 is replacedor supplemented with an optical interference filter that blocks “stray”light at angles of incidence that are relatively far from normal to theimaging plane. Multilayer optical filters can be used that transmitlight at incidence near normal in much the same way such a filter can beconstructed to only transmit light at specific wavelengths. Althoughsuch an angle-specific filter may be designed to work for specific lightwavelengths, such an interference filter may be used to reject the straylight coming from adjacent ridges and valleys.

The collimator filter layer 204 may also be a transparent glasscollimator filter with round openings on top and bottom. This type ofcollimator filter layer is made using double-sided alignment techniqueto create top and bottom openings that are aligned, but withoutphysically hollow holes through the glass body. The top surface of thecollimator filter layer can be textured to be a diffuser for the lightentering while the bottom surface can be metallic to recycle byreflecting the light back to the transparent glass body. One of theadvantages is that this method makes lamination simpler since there areno physically hollow apertures. With this glass collimator filter layer,cover glass, light guide film, and glass filter can be laminated withreadily available lamination equipment.

In some embodiments, an opaque glass collimator filter with drilledapertures can be used. This is similar to the previously describedcollimator filter film. The manufacturing method may be the same, exceptfor the fact that the body is glass. The aperture density is determinedbased on the required dpi.

FIG. 6 shows a method 600 of imaging in accordance with the presentdisclosure.

In step 602, the sensing region is illuminated using an illuminationlayer having a light source and/or light guiding element. As previouslydescribed, this may be done by using a light source directing light intoa separate light guiding element or by transmitting light directly intothe cover layer. The transmitted light is directed towards a sensingregion above the cover layer and reflected from the object towards thelight collimator layer.

In step 604 some of the reflected light is blocked at the collimatorfilter layer while other light passes through apertures in thecollimator filter layer. Generally, light rays at relatively near normalincidence to the collimator filter layer will pass through the apertureswhile light rays further from normal incidence will be blocked. Lightmay be blocked by the top surface of the collimator layer, anintermediate layer of the collimator, a bottom layer of the collimator,or sidewalls of the collimator aperture.

In step 606, the light which passes through the collimator filter layerbecomes incident on one or more optical sensing elements on the sensorarray below the light collimator layer. In instances where more than onesensing element is below a particular aperture in the collimator filterlayer, the detected light at the sensing elements may be averaged orotherwise combined. The image data may be adjusted to account forsensing elements that are not below an aperture.

In step 608, the detected light at the image sensor array is processedto form an image or a partial image of the input object. Such processingmay include, for example, stitching partial images together, relatingvarious partial images to one another in a template, and/or comparingcaptured image data to previously stored image data as part of anidentification or verification process.

Although this invention describes optical object imaging in the contextof fingerprint image sensing, the method and system may be used to imageany object. For example, a high resolution image of a palm or hand maybe acquired by placing the hand directly on the cover layer. Imaging ofnon-biometric objects is also with the scope of this disclosure.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminate theinvention and does not pose a limitation on the scope of the inventionunless otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element as essential to thepractice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. An optical fingerprint sensor, comprising: an image sensor array; acollimator filter layer disposed above the image sensor array, thecollimator filter layer having an array of apertures; and anillumination layer disposed above the collimator layer.
 2. The opticalfingerprint sensor of claim 1, wherein the image sensor array is formedin a semiconductor die.
 3. The optical fingerprint sensor of claim 1,wherein the image sensor array includes a plurality of optical sensingelements, and the plurality of optical sensing elements receive lightreflected from a sensing region and transmitted through an aperture ofthe array of apertures.
 4. The optical fingerprint sensor of claim 1,wherein a ratio of a height of the apertures to a diameter of theapertures is between about 3:1 and 100:1.
 5. The optical fingerprintsensor of claim 1, wherein a ratio of a height of the apertures to adiameter of the apertures is between about 5:1 and 20:1.
 6. The opticalfingerprint sensor of claim 1, further comprising a blocking layerdisposed above the collimator filter layer, the blocking layerconfigured to permit transmission of non-visible light from theillumination layer and block transmission of visible light.
 7. Theoptical fingerprint sensor of claim 1, wherein the collimator filterlayer includes a top surface having a reflecting layer.
 8. The opticalfingerprint sensor of claim 1, wherein the collimator filter layercomprises a cured polymer.
 9. The optical fingerprint sensor of claim 1,wherein the array of apertures have a pitch less than a pitch of ridgesin a fingerprint.
 10. An optical fingerprint sensor, comprising: anillumination layer configured to direct light to a sensing region; acollimating layer, disposed below the illumination layer, and includinga plurality of apertures, wherein the apertures are configured to blocka portion of light from the illumination layer; and an image sensorlayer, disposed below the collimating layer, and including an array ofoptical sensor elements arranged so that a plurality of the sensorelements receive light transmitted through one of the plurality ofapertures.
 11. The optical fingerprint sensor of claim 10, wherein theplurality of apertures have a pitch less than a pitch of ridges in afingerprint.
 12. The optical fingerprint sensor of claim 10 wherein aratio of a height of the apertures to a diameter of the apertures isbetween about 3:1 and 100:1.
 13. The optical fingerprint sensor of claim10, wherein a ratio of a height of the apertures to a diameter of theapertures is between about 5:1 and 20:1.
 14. The optical fingerprintsensor of claim 10, further comprising a blocking layer disposed abovethe collimating layer, the blocking layer configured to at leastpartially permit transmission of light from the illumination layer andat least partially block transmission of other light.
 15. The opticalfingerprint sensor of claim 14, wherein the blocking layer is opaque.16. The optical fingerprint sensor of claim 14, wherein the blockinglayer is semitransparent.
 17. A method of imaging a fingerprint using adevice, comprising: transmitting light in an illumination region suchthat at least a portion of light reflects from a sensing region;blocking at least a first portion of the light reflected from thesensing region at a surface of a collimating layer; blocking at least asecond portion of the light reflected from the sensing region within aplurality of apertures of the collimating layer; and sensing, at aplurality of optical sensor elements in a sensor array, a third portionof light reflected from the sensing region, the third portion of lightbeing passed through at least one of the plurality of apertures in thecollimating layer.
 18. The method of claim 17, wherein data receivedfrom the plurality of sensor elements is combined into a single pixelvalue.
 19. The method of claim 17, further comprising eliminating datafrom unused optical sensing elements.
 20. The method of claim 17, wherethe step of transmitting light in an illumination region comprisestransmitting light in a cover layer.